Various emergency communication systems have been developed for use by publilc service organizations, such as the police and fire departments, and for use by private security organizations in guarding industrial sites, plants, hospitals and other buildings. One such system, entitled "Emergency Communication System", is described, for example, in U.S. Pat. No. 3,914,692 issued to George C. Seaborn, Jr. on Oct. 21, 1975, and entitled EMERGENCY COMMUNICATION SYSTEM. The system includes a portable transmitter-receiver unit which is carried by an individual for transmitting an emergency message and for notifying the individual of receipt of the transmitted message at a remote station. Typically in such a system, the emergency message transmitted by the portable unit is received at a local station (e.g., a two-way radio station located nearby) and relayed or transmitted from the local station (via radio or telephone link) to a remote station or central office. A radio receiver or modem at the remote station receives the relayed message and forwards this message to a nearby computer which logs or prints the message for human perusal and action. The computer then sends to the local station, via the telephone link or via a radio transmitter, an acknowledgement (ACK) message verifying receipt of the emergency message. The local station transmits the ACK message to the portable unit, which activates an indicator notifying the individual that the emergency message has been received at the remote station.
Although such systems provide for transmission of emergency messages from a device on the person and for notifying the person of receipt of the transmitted messages at a remote station, their use is often limited to businesses and public and private security organizations which require and can afford such elaborate communications equipment (i.e., equipment responsive to computer-generated acknowledgement signals from the remote stations). To the average individual, however, such systems are often too costly and too elaborate to be acquired mainly for signalling (from one's person) an emergency condition and obtaining notification of receipt of the signalled condition. What would be useful to a larger segment of the population (viz., to individuals in addition to businesses and public and private security organizations), therefore, is an inexpensive, emergency communication system that could be added-on, without modification and without the requirement of FCC (Federal Communications Commission) approval, to existing two-way radio systems such as CB (citizen's band) vehicular radio systems. One such add-on type system is described, for example, in U.S. Pat. No. 3,723,876 issued Mar. 27, 1973 to George C. Seaborn, Jr. and entitled EMERGENCY DISTRESS SIGNALING SYSTEM. However, a fundamental deficiency of such a system is that, although it provides the economical add-on feature, it does not provide individuals with a means of obtaining notification of receipt of their transmitted messages.
What is needed, therefore, is an emergency communication system that could be added to a conventional two-way radio system such as a CB radio system, and that could notify an individual (via a portable transmitter-receiver unit carried by the individual) of receipt of emergency messages transmitted by the individual. The added system should not require modification of the CB radio system and, hence, should not require FCC approval. Furthermore, to provide greater flexibility of use, the system should enable the user (transmitter) to select the method for acknowledging receipt of the messages, rather than being responsive only to computer-generated acknowledgement signals.